In multicast/broadcast over infrastructure-based/cellular wireless networks (e.g. 3G cellular networks, WiMax, WLANs or Digital Video Broadcasting (DVB)), data are transmitted to multiple receivers/wireless devices from a base station/access point/central station/host/server. In this specification, where “/” is used, it is intended to give alternative names or descriptions for the same component or device. That is, it is intended as the word “or”. Compared to multiple unicast sessions of the same data to each receiver individually, multicast greatly improves the network efficience to distribute data to multiple devices in wireless networks, especially thanks to the shared nature of wireless media (the data could be simutaneously received by any receiver within the sender's communication range). However, it is difficult to guarantee the receiving reliability of multiple multicast/broadcast receivers because the wireless links are unreliable and multiple receivers experience heterogeneous channel conditions. The multicast/broadcast services in many networks such as DVB and 3G multimedia broadcast/multicast services (MBMS) do not provide the reverse communications channel for the receivers to request the retransmission of lost data packets. Furthermore, the radio resource/bandwidth is generally expensive in infrastructure-based networks because the deployment is costly and the spectrum may be licensed. Therefore, it is a key and challenging task to support good quality of multicast service for the multiple receivers while efficiently utilizing radio resources and improve the throughput and coverage of the infrastructure-based/cellular wireless networks.
In many wireless multicast/broadcast systems, the forward error correction codes (FEC) are used within a packet at the physical layer to protect against multipath fading and interference and reduce packet errors. To recover the lost packets in wireless networks, the FEC codes are also applied across packets at the transport and application layers. However, wireless channel conditions are time-varying and multiple receivers in multicast environments experience heterogeneous channel conditions. In the prior art, FEC codes are used according to the worst channel conditions to ensure the receiving quality of all the receivers in the desired service area. This results in a large overhead and requires a great deal of radio resources in infrastructure-based multicast networks. Another prior art technique to improve reliability and throughput is to use multiple antennas. However, this approach incurs high cost and complexity to the wireless systems including the base station and wireless devices.
Recently there has been some work to improve the quality, throughput, and coverage of a cellular network with assistance of an ad hoc network. In a recently reported system, mobile stations with good link quality with the base station act as relays for stations with poor link quality with the base station. In this system, a single wireless interface is used for both relay and infrastructure modes. Thus, the total cell throughput achieved in this hybrid-mode network is bounded by the available cellular bandwidth. In another recently reported system, two types of wireless interfaces are used to integrate cellular and ad hoc networks, in which high-bandwidth wireless channels in ad hoc mode (IEEE 802.11) relay the unicast traffic of the cellular network (3G) for improving cellular throughput and coverage range. In yet another recently reported system, the multicast data is transmitted to a relay node over a short range within the cellular network (3G) and is forwarded to the remaining subscribing nodes by the relay node via high speed ad hoc networks (IEEE 802.11). All the above approaches use a relay node to forward the cellular traffic to the destination nodes via the ad hoc network whether the cellular network and the ad hoc network use a single wireless interface or two types of wireless interfaces. The downlink data is sent to the relay node from the base station and then forwarded to the destination nodes via a single or multi-hop path in the ad hoc network. The uplink data (if there is any) goes through a reverse path. That is, the destination nodes always receive or transmit data through the relay nodes in the ad hoc network path. In the above approaches, the relay node always helps the destination nodes. There is no cooperation between the nodes/wireless devices. This is not fair for the relay node. The relay node consumes much more CPU power and battery energy (if the relay node is operated by battery). The requirement for the ad hoc network resources such as bandwidth around the relay node is also high while the network resources in other portions of the ad hoc network may sit idle.
The problem solved by the present invention is how to design a system resilient to packet loss for high-quality multicast/broadcast services over wireless networks, and improve the throughput, quality, and coverage range of the infrastructure-based wireless networks. Thus, the present invention solves the above problems.